Load centers and other electrical distribution devices are commonly used in residential, commercial, and industrial applications. Individual circuit interrupters are mounted within these devices to protect branch circuits against overload and fault conditions. Basically, circuit interrupters like circuit breakers and fusible switches comprise a pair of separable contacts, a spring-operated mechanism for effecting separation of the contacts, and a tripping mechanism or fuse which automatically releases the operating mechanism upon occurrence of an overload or fault condition. Electrical connection to the circuit breakers, as well as other electrical distribution devices, are usually provided by load and line terminals designed to accept copper or aluminum single or stranded wire.
A problem can arise in providing proper mechanical and electrical contact between the terminal and wire during both normal and shorting conditions of the circuit breaker. Most terminals are a combination of a threaded screw and clamp plate. The bottom most threads of the screw are usually upset to prevent the screw from disengaging from or backing out of the terminal during wire installation. Upsetting some of the threads on the screw to retain the screw with the terminal leaves only enough depth on the screw to engage one or two threads with the clamp plate in the "hold area" of the terminal. As increasing torque is applied to the screw to secure the wire against the clamp plate, the threads on the screw or in the clamp plate may be stripped. The torque stripout value of the screw and terminal is occasionally below the minimum value needed for adequate connection between the wire and terminal.
The need arises to provide a clamp plate assembly for the terminal of electrical devices which does not upset screw threads to retain the screw with the clamp plate during wire installation. Providing more threads or "holding area" on a clamp plate assembly can improve torque stripout value well in excess of the minimum value needed for adequate connection between the wire and terminal. Furthermore, the clamp plate assembly should be inexpensive to manufacture and easy to install.